1. Technical Field
The invention relates to a probe apparatus for use in moving-medium type memory device, in which minute probes are actuated by electrostatic force or by the force generated by a bimorph. More particularly, the invention relates to a probe apparatus of the forgoing type, in which misalignment of conductive needles associated with said probes is minimized or eliminated.
2. Description of the Prior Art
In recent years, various types of moving-medium type memory devices using minute probes have been proposed in place of hard-disk memories and semiconductor memory devices, such as CMOS devices (see Japanese Patent Application Kokai No. 4-98120, J. Sliwa, Jr., Microvibratory Memory Device, Japanese Patent Application Kokai No. 4-289580 (U.S. Pat. No. 5,216,631, issued Jun. 1, 1993), and Japanese Patent Application Kokai No. 4-364299). Such memory devices use scanning probe microscope technology, where bimorph-actuated long flat-plate-form cantilevers are used as probes. The reading and writing of data from and into the recording medium is performed using these cantilevers.
FIG. 1 shows an outline of a conventional moving-medium type memory device. The memory device shown in FIG. 1 consists of a probe apparatus 100, a memory substrate 200, a control circuit 300, and a write-read circuit 400. A plurality of cantilever type probes 101 which have conductive needles 102 formed on their tip ends, and which are actuated by a bimorph force, are formed on the surface of the probe apparatus 100. A memory medium 201 is formed on the surface of the memory substrate 200, and electrodes 202 that are used for reading and writing are formed beneath this memory medium 201. The probes 101 are actuated by signals sent to said probes 101 from the control circuit 300, and the write-read circuit 400 performs the reading and writing of data in the memory medium 201 by applying a write-read voltage across the conductive needles 102 at the tips of the probes 101 and the electrodes 202.
If the length of the probes 101 is too short, the distance of movement of the conductive needles 102 formed on the tips of said probes 101 with respect to the memory medium 201 cannot be set at a large value. Conversely, if the length of the probes 101 is too long, the conductive needles 102 tend to bend in the direction perpendicular to the direction of length of the probes 101 and parallel to the memory medium 201, i.e. in the horizontal direction, so that misalignment of the conductive needles 102 occurs. Furthermore, when the probes 101 are actuated, the probes necessarily bend in the direction of actuation, so that misalignment of the conductive needles 102 occur in the direction of length of the probes 101.
If the recording region (area) per bit is reduced to a small value, reading and writing errors tend to occur as a result of the above mentioned misalignment, so that the reliability of the system drops. Accordingly, to prevent such a drop in reliability, it is necessary to increase the size of the recording region. However, this leads to a new problem, i.e. an increase in the data recording density is prevented by the use of such a large recording region.